Geographic Range

The entire population of the Hainan black-crested gibbon, Nomascus hainanus, is found in the 300 km^2 Bawangling National Nature Reserve (BNNR) on Hainan Island off of the coast of China. Historically, N. hainanus was widespread on Hainan Island but a recent estimate put its entire geographic range as low as 14 to 16 km^2 of BNNR. (Zhang, et al., 2010; Zhou, et al., 2005)

Habitat

Hainan black-crested gibbons live in tropical primary forests. It is estimated that 95% of their original habitat has been lost. Hainan black-crested gibbons require indigenous forest of Hainan Island and do not inhabit recently planted pine forests or rubber plantations. Due to habitat loss and hunting, this species has shifted its primary habitat from lowland forest to higher mountainous forest (with elevations ranging from 100 to 1800 m on Hainan Island). Optimal habitat is hard to determine as a result of the small population size and altered environment on the entire island. However, mature, ravine tropical forests, in particular, seem to be favored. Like other gibbons, Hainan black-crested gibbons are specialized for living in the canopies of forests. (Zhang, et al., 2010; Zhou, et al., 2008)

Physical Description

Adult males and juveniles have completely black pelage while females are brownish buff with some black hairs appearing on the limbs as they age. Males and females have a large black crest of fur on the top of their heads. The crest is approximately 10 by 3 cm. Females also have a characteristic white face ring. Infants are born tawny brown, becoming black within 5 to 6 months. (Liu, et al., 1989; Mootnick and Fan, 2011)

Adults weigh between 5.8 and 10 kg. Hind limbs are 70.4% the length of forelimbs, which is slightly longer than in other black-crested gibbons (Nomascus species). The interorbital distance ranges from 10.4 to 10.7 mm. Along with pelage coloration, physical size is the main identifying characteristic of Nomascus species. Due to the rarity of Hainan black-crested gibbons, very few specimens have been collected and little is known of variation in size. However, within gibbons there is little variation in body size. Most likely N. hainanus has a similar body length as other gibbons and this assumption is supported by anecdotal evidence (Pocock 1905). Lar gibbons (Hylobates lar) are reported to reach an adult size of 42 to 60 cm in length (excluding the tail). (Ma, et al., 1988; Pocock, 1905; Uhlenbroek, 2011; Zihlman, et al., 2011)

Reproduction

Social polygyny, with two females and a single male, is the usual mating system in N. hainanus. Females initiate mating by approaching a male and moving their head and limbs in rhythmic, jerky motions. Multiple copulations via dorsoventral mounting may occur in a single day. Sexually active females occasionally engage in post-conception copulation, which is relatively rare amongst the primates. (Zhou, et al., 2008)

The amount of time between births is approximately 24 months. This timing may be caused by biannual fruiting of many favored food sources and thus link reproduction with the abundance of food. Two females in a single social group may rear offspring from the same male at the same time. Gestation has been estimated to be 136 to 173 days. (Mootnick, et al., 2012; Zhou, et al., 2008)

Infants are dependent on their mother for the first 1.5 years of their lives, but remain in the social group as juveniles for some time after this. It is during this infant dependency period where lactation occurs. Lactation is energetically costly for female gibbons of other species. (Lappan, 2009; Zhou, et al., 2008)

In one case, a maturing male offspring was driven out of the group at 5.5 years of age. This is quite early compared to most other gibbon species, which mature from 6 to 9 years. A possible reason for this eviction, besides actual sexual maturity is that, due to limited resources, the alpha male may have been forced to drive out the maturing offspring. (Tilsen, 1979; Zhou, et al., 2008)

Behavior

Hainan black-crested gibbons are found in social groups composed of females, juveniles, infants and, occasionally, males. Males will also live solitarily. Group size has been hard to determine due to the extremely low population size and fluctuations in behavior of N. hainanus as a result of the degradation of habitat. (Zhou, et al., 2005)

The most common form of locomotion in a closely related species of black crested gibbon (Nomascus concolor concolor) is brachiation (rapid swinging from branch to branch via the forelimbs) through the canopy. Leaping, walking and climbing were also observed but the gibbons were never seen to come to the ground. Brachiation has also been observed in N. hainanus. (Haimoff, 1984; Haimoff, 1987)

Home Range

Nomascus hainanus individuals occupy home ranges of 200 to 500 hectares (2 to 5 km^2), which are the largest home range sizes of any gibbon. However, this large size might be the result of reduced intraspecific competition or increased area between suitable food patches. It is suggested that home range size might recently have increased to nearly 1000 hectares (10 km^2) due to degradation of habitat quality. (Zhang, et al., 2010; Zhou, et al., 2005; Zhou, et al., 2008)

Communication and Perception

Hainan black-crested gibbons often perform morning duets between male and female pairs. The female usually only emits a single loud noise often referred to as a great-call. The male’s song is more elaborate and has at least three distinct calls. The presence of a laryngeal sac in males may contribute to the increased complexity of vocalizations. Hainan black-crested gibbons are believed to be the only gibbon species with a male dominated duet. (Haimoff, 1984)

Hainan black-crested gibbons are one of only three gibbon species in which the female makes vocalizations during mating. There are many hypotheses concerning these soft grunts of the female but it might have be related to the social polygyny of N. hainanus and it may be an advertisement of ovulation to other females. (Zhou, et al., 2008)

Food Habits

Hainan black-crested gibbons are almost exclusively frugivores. In the refuge they inhabit, the most common food sources are the fruits from Litchi canensis, Nephelium topengii, and various Ficus species. Figs in particular have been noted as a favored food source. Closely related species of gibbons eat insects, seeds, and grains and N. hainanus may have a similar diet. (McConkey, 2005; Zhou, et al., 2008)

Predation

Tree selection for sleeping is an antipredator behavior for gibbons. They often sleep in the tallest trees in an area which would safeguard them from most terrestrial predators. Gibbons also sleep on branches with many twigs so that the twigs, which vibrate easily, will act as an early warning system. Hainan black-crested gibbons were not explicitly mentioned in a Fei et al. 2012 study, but these insights into their close relatives, N. nasutus, may hold true for them as well. (Fei, et al., 2012)

Two attacks from an unidentified species of hawk lasting approximately 15 minutes have been observed on N. hainanus. A species survey of Hainan Island recorded 7 species of carnivorous eagles and hawks. (Li, et al., 2013; Zhou, et al., 2005)

Humans are the main predators of Hainan black-crested gibbons. Humans can benefit by selling adults into the illegal animal trade, use the meat for food, or sell the bones for use in traditional Chinese medicine. Mass slaughters have been recorded on numerous occasions. (Zhou, et al., 2005)

Ecosystem Roles

Hainan black-crested gibbons have been described as an umbrella species for the local ecosystem. An umbrella species is one which indicates the overall health of an ecosystem. Gibbons may also play a role in the seed dispersal of many of the fruits that they eat. (McConkey, 2005; Zhang, et al., 2010)

Ecosystem Impact

disperses seeds

Economic Importance for Humans: Positive

Hainan black-crested gibbons can act as seed dispersers for forest tree species. Trade in live N. hainanus as well as body parts, can result in hefty profits from black market Chinese medicine. There is no proven efficacy of these traditional "medicines" and the impact on wildlife populations is devastating. (McConkey, 2005; Zhou, et al., 2005)

Economic Importance for Humans: Negative

Due to the critically endangered status of Hainan black-crested gibbons, the Chinese government has put a ban on all types of forestry in or around BNNR. Hainan Island, which is home to many introduced rubber plantations, has been forced to stop the expansion of the rubber industry in order to save N. hainanus and other endangered species. This is a short-term negative economic impact, but has long-term positive impacts because it helps to protect a critical and unique ecosystem. (Zhou, et al., 2005; Zhou, et al., 2008)

Conservation Status

The IUCN currently lists Hainan black-crested gibbons as critically endangered. Some have suggested that they are the rarest mammals in the world, with approximately 20 individuals counted in a recent survey. A major concern is that of the approximately 20 individuals left, only 4 are adult females and one of these may be post-reproductive. Numbers have increased since 2003, when it was believed that there were as few as 13 individuals. (Mootnick, et al., 2012; Zhou, et al., 2005)

Conservation efforts are varied. Technologies such as remote sensing and geographic information systems are being used to determine suitable habitats. The government is also planning on adding to the list of protected forest on Hainan Island. In 2003, the Hainan Gibbon Action Plan was launched. Population surveys, reforestation, and the training of staff to monitor the gibbons are all parts of the Action Plan. (Mootnick, et al., 2012; Zhang, et al., 2010)

Habitat loss and human encroachment and activity are the main reasons for the decline in population of Hainan black-crested gibbons. The species has seen a drastic reduction in range and population since the 1950s. The annual rate of habitat loss is approaching zero, although more work needs to be done concerning critical habitat conservation, but Hainan black-crested gibbons are, without a doubt, on the very edge of extinction. (Zhang, et al., 2010)

Other Comments

It is important to note that N. hainanus and most other gibbon species are in the midst of controversy concerning their classification. By the 1980s, Ma et al. reported that N. hainanus has been known as Hylobates hainanus, Hylobates pileatus, Hylobates concolor concolor and was then known as Hylobates concolor hainanus. Wei et al. noted that since the 1980s the species has been known as Nomascus concolor, Nomascus nasutus, and Hylobates (Nomascus) hainanus. Wei et al referred to the species as Nomascus sp. cf. Nasutus hainanus. The species is now known as Nomascus hainanus based on morphological, vocal, and genetic characters. (Ma, et al., 1988; Mootnick and Fan, 2011; Mootnick, et al., 2012; Wei, et al., 2004)

There are currently four genera of gibbons; Hoolock, Hylobates, Nomascus, and Symphalangus. Each genus differs in the number of chromosomes, with all six species of Nomascus having 52. Zihlman et al. believe that the distribution of body mass can also be used to classify species into these genera. (Zihlman, et al., 2011)

Contributors

Rob Gregoire (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

acoustic

uses sound to communicate

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

diurnal

active during the day, 2. lasting for one day.

drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

duets

to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

island endemic

animals that live only on an island or set of islands.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

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This material is based upon work supported by the
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Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.